The present invention relates to automatic transfer switches for three-phase power supplies.
In data centers, electrical and computer equipment (e.g., servers) is commonly mounted in racks. To achieve power redundancy, some data centers bring two sources of power to each server-filled rack, a primary power source and a secondary power source. Historically, these power sources have provided single phase (i.e. having two conductors) power. Automatic Transfer Switches (ATSs) are used in such dual-power systems to switch the power from the primary to the secondary source when the primary power source has degraded or is interrupted or lost. Under normal circumstances, the ATS connects all the servers in the rack to the primary power source. When the primary source is interrupted (i.e., a black out) or its quality has degraded (i.e., a brown out), the ATS switches the servers to the secondary power source. During the transition from the primary to the secondary power source, there is a brief period of time when the powered devices (e.g. servers) have no power, and that time is the “energy gap.” Most devices can withstand a very short energy gap (e.g. about 10-20 milliseconds) which is longer than the period of time that it takes for a single-phase ATS to switch power sources (e.g. about 7-9 milliseconds).
As the density of equipment in a single rack has increased, the amount of power required for a single rack's worth of equipment can exceed the amount that one single-phase power line can supply. Accordingly, three-phase power sources (i.e. having three or four conductors) are now being used to supply a single rack's worth of equipment. As with single-phase power sources, primary and secondary three-phase power sources are being used to provide redundancy along with three-phase ATS units (FIGS. 1, 2). However, three-phase ATSs require a longer period of time (about 16-20 milliseconds) than single-phase ATSs to switch from the primary to the secondary power source. As a result, many servers and other devices completely lose power during the transition, as described further hereafter. Complete loss of power, sometimes referred to as dropping of a load, causes equipment such as servers to abruptly shut down, leading to loss of data and computing capacity.
Thus, there is a need for an ATS for three-phase power sources that reduces the output energy gap of known three-phase ATSs. Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.